Zinc aluminum mercury anode for electrodeposition of zinc



- baths.

Patented Nov. 15, 1932 UNITED STATES PATENT OFFICE GEOBGE B. HOGABOOM, OF NEW BRITAIN, CONNECTICUT, ASSIGNOR TO- HANSON-VAN WINKLE-MUNNING COMPANY OF MATAWAN, NEW JERSEY, A CORPORATION OF NEW JERSEY zmc arummm mcuar mom". son ELEcraoDErosrrIoN or zmo 80 Drawing.

This invention relates to anodes for use in the electrodeposition of zinc in both acid and cyanide baths.

Modern practice in the electrodep'osition of metals from solution recognizes important advantages in supplying the metal and maintaining the composition of the electrolyte by the employment of soluble anodes of the metal to be deposited. The use of soluble anodes is usually more economical than introducing the metal in the form of soluble salts of themetal, and furthermore tends tomaintain the metal content and acidity of the bath more uniform. In the electrodeposition of zinc from acid baths, for example, the use of pure zinc an-.

odes, which are soluble in the bath, has led to certain difliculties due partly to the fact that such an anode is chemicallf soluble in the bath even when no external voltage is applied, with the result that a serious loss of metal occurs during idle periods, and even during the electroplating operation the corrosion or solution of the anode occurs at a greater rate than the deposition of the metal upon the cathode. Consequently, the metal content of the bath increases and the acidity of the bath diminishes. efiiciency of pure zinc anodes may in a'given case be in the neighborhood of 107%, and suspended particles of metal or sludge freed from the anode find their way to the cathode where they adhere as inclusions to the detriment of the electrodcpos t both with respect to' its appearance and with respect to its protective quality on the article being plated. The indicated cathode efiiciency due to such inclusion is also frequently found to be higher than 100%. Many of the disadvantages of pure zinc anodes in acid baths are also present to some extent in the use of such anodes in cyanide.

My invention has for its object to provide an improved soluble anode for use in the electrodeposition of zinc, from either acid or cyanide baths.

In accordance with my invention, the anode comprises zinc with small additions of aluminum and mercury. The zinc, aluminum and mercury are preferably fused together as Application 11166 February 20, 1981.

The indicated anode Comparative tests of Serial No. 517,306.

a small quantity of mercury has already been.-

described in the U. S. patent to Abraham Van Winkle, No. 901,758, granted October 20,1908. I find that by including aluminum in the composition, equal or better results are obtained with less mercury than is the case with zinc mercury anodes which do not include aluminum in their com osition.

The addition of small quantities of aluminum and mercury to zinc confers upon the anode important chemical and electrochemical properties. It reduces the rate of chemical solution of the anode, reduces the indicated anode efliciency, reduces the formation of sludge, improves the grain structure of the anode, causes the anode to corrode more evenly, brings about an approximate equalization of anode and cathode efliciencies without the occurrence of objectionable inclusions of sludge and suspended matter in the electrodeposit, and maintains the metal content and acidity of the solution'much more uniform than in the use of pure zinc anodes. The electrodeposit, when using zinc anodes containing aluminum and mercury, is of better appearance and texture and offers better protective properties on the electroplated article.

pure zinc, zinc with additions of mercury and zinc with additions of aluminum and mercury, showed in acid baths, for example, an anode efliciency ranging from 106% to 107.6% in the case of pure zinc, an anode efliciency of 100.2% to 100.8% in the case of zinc with additions of from .2 to .3% mercury, an anode efliciency ranging from 99.1% to 99.7% in the case of .zinc with .5% aluminum and from .1% to .3% mercury, and an anode efiiciency rangin from 98.3% to 98.6% in the case of zinc with 1% aluminum anodes composed of and from .1 to 2% mercury. Thus the presence of aluminum in the composition reduces the anode efiiciency to 'avgiven value with less mercury. The presence of aluminum and mercury in the zinc anode reduced the cathode efficiency from an average value of 101.7% for three samples of pure zinc to values ranging from 98.9% to 100.4%,-

or practically to equality with the anode eifi-. o ciency. Anodes of zinc with small additions of aluminum and mercury showed no evolution of gas on standing idle in the solution, whereas pure zinc anodes showed a substantial evolution of gas under such conditions. The metal content of the solution showed after forty-eight hours run a large increase when using pure zinc anodes, a considerable decrease when using anodes of zinc with additionsof from 2% to 3% mercury, and a lower decrease in metal content when using anodes with additions of from .5% to 1% aluminum, and from .1% to 3% mercury.

In the same time the acidity of the bath showed substantial decrease when using pure zinc anodes, and negligible or even a slight increase when using anodes of zinc with I small additions of aluminum and mercury.

The grain structure on corrosion of the anode was coarse in the case of pure zinc, whereas the surface was smooth and practically free from granular appearance in the case of anodes composed of zinc with small additions of aluminum and mercury. The sludge formation, while heavy in the case of anodes 85 of pure zinc, was either greatly reduced or,

entirely absent in the case of anodes composed of zinc with small additions of aluminum and mercury. Each test was conducted with the anode and cathode areas equal.

From the above observations it will be seen that the various factors are subject to control by varying the proportions of aluminum I and mercury to zinc in the anode. It has been found that the results which are desired are in most cases obtained by the use of as low as .5% aluminum and .1% to .3% mercury in the zinc anodes.

- I claim 1. A zinc anode having aluminum and mercury contents in amounts less than 5% aluminum and less than 1% mercury.

2. A zinc anode having aluminum and mercury contents in amounts less than 1% aluminum and from .1% to .3% mercury.

3. A zinc anode containing \in the neigh borhood of .5% aluminum and 2% mercury.

GEORGE B. HOGABOOM. 

